Method for depositing a multilayer barrier coating on a plastic substrate

ABSTRACT

The present invention is a plastic container coated with a multi-layer barrier coating. The multi-layer barrier coating is useful for providing an effective barrier against gas permeability in containers and for extending shelf-life of containers, especially plastic evacuated blood collection devices.

This is a divisional of U.S. Ser. No. 08/593,976 filed Jan 30, 1996, nowU.S. Pat. No. 5,955,161.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a multi-layer barrier coating for providing aneffective barrier against gas and water permeability for containers,especially plastic blood collection tubes.

2. Description of the Related Art

With the increased emphasis on the use of plastic medical products, aspecial need exists for improving the barrier properties of articlesmade of polymers.

Such medical products that would derive a considerable benefit fromimproving their barrier properties include, but are not limited to,collection tubes and particularly those used for blood collection.

Blood collection tubes require certain performance standards to beacceptable for use in medical applications. Such performance standardsinclude the ability to maintain greater than about 90% original drawvolume over a one year period, to be radiation sterilizable and to benon-interfering in tests and analysis.

Therefore, a need exists to improve the barrier properties of articlesmade of polymers and in particular plastic evacuated blood collectiontubes wherein certain performance standards would be met and the articlewould be effective and usable in medical applications.

SUMMARY OF THE INVENTION

The present invention is a plastic composite container with multipleorganic and inorganic coating materials disposed over the outer or innersurface of the previously formed composite container. Desirably, thebarrier coating materials comprise a first layer of a polymeric materialapplied to the outer surface of the previously formed compositecontainer, a second layer comprising a sequence of coatings comprisingorganic and inorganic materials applied over the first layer and a thirdlayer of an organic material applied over the second layer.

The first layer, a primer coating, is preferably a highly crossed linkedacrylate polymer. The coating may be formed either on an interiorsurface portion, on an exterior surface portion, or both of thecontainer.

The second layer is preferably a sequence of multiple organic andinorganic coatings. Prefereably, the sequence of the coatings may beexpressed as follows: ##EQU1## where n=0-10.

Most preferably the inorganic coating is a silicon oxide basedcomposition, such as SiO_(x) wherein x is from 1.0 to about 2.5; or analuminium oxide based composition. Most preferably, the organic coatingis a highly crossed linked acrylate polymer.

Optionally, a third layer of a barrier coating, preferably an organicbarrier composition, such as poly (vinylidene chloride) (PVDC), is mostpreferably applied over the second layer.

Preferably, the primer coating is a blend of monoacrylate (i.e.,isobornyl acrylate) and diacrylate monomers (i.e., an epoxy diacrylateor a urethane diacrylate) as described in U.S. Pat. Nos. 4,490,774,4,696,719, 4,647,818, 4,842,893, 4,954,371 and 5,032,461, thedisclosures of which are herein incorporated by reference. The primercoating is cured by an electron beam or by a source of ultravioletradiation.

Desirably, the first layer is formed of a substantially cross linkedcomponent selected from the group consisting of polyacrylates andmixtures of polyacrylates and monacrylates having an average molecularweight of between 150 and 1,000 and a vapor pressure in the range of1×10⁻⁶ to 1×10⁻¹ Torr at standard temperature and pressure. Mostpreferably, the material is a diacrylate.

Preferably, the thickness of the acrylate primer coating is about 0.1 toabout 10 microns and most preferably from about 0.1 to about 5 microns.

A desirable second layer which is disposed over the first layerpreferably comprises a sequence of multiple coatings comprising asilicon oxide based composition, such as SiO_(x), that is desirablyderived from volatile organosilicon compounds and acrylate.

The silicon oxide based composition provides a dense, vapor-imperviouscoating. Preferably, the thickness of the silicon oxide based coating isabout 100 to about 2,000 Angstroms (Å) and most preferably from about500 to about 1,000 Å. A coating above 5,000 Å may crack and therefore beineffective as a barrier.

The acrylate provides a platform for deposition of the inorganiccoating. Preferably, the thickness of the acrylate coating is about 0.1microns to about 10 microns and most preferably from about 0.5 micronsto about 3 microns.

An optional third layer may be disposed over the second layer andpreferably comprises vinylidene chloride-methylmethacrylate-methacrylate acrylic acid polymer (PVDC), thermosettingepoxy coatings, parylene polymers or polyesters.

Preferably, the thickness of the PVDC layer is about 2 to about 15microns and most preferably from about 3 to about 5 microns.

The process for applying the first layer to a container is preferablycarried out in a vacuum chamber wherein a curable monomer component ismetered to a heated vaporizer system where the material is atomized,vaporized and condensed on the surface of the container. Followingdeposit of the monomer onto the surface of the container, it is cured bysuitable means such as electron beam curing. The deposition and curingsteps may be repeated until the desired number of layers has beenachieved.

A method for depositing a silicon oxide based coating is as follows: (a)pretreating the first layer on the container with a first plasma coatingof oxygen; (b) controllably flowing a gas stream including anorganosilicon compound into a plasma; and (c) depositing a silicon oxideonto the first layer while maintaining a pressure of less than about 500microns H_(g) during the depositing.

Although the pretreatment step is optional, it is believed that thepretreatment step provides for improved adherence qualities between thesecond layer and the first layer.

The organosilicon compound is preferably combined with oxygen andoptionally helium or another inert gas such as argon or nitrogen and atleast a portion of the plasma is preferably magnetically confinedadjacent to the surface of the first layer during the depositing, mostpreferably by an unbalanced magnetron.

The PVDC layer is applied over the second layer by dipping or sprayingand then followed by air drying at about 50° C.

Most preferably, the method for depositing a barrier coating on asubstrate, such as a plastic collection tube comprises the followingsteps:

(a) selecting a curable component comprising: i) polyfunctionalacrylates, or ii) mixtures of monoacrylates and polyfunctionalacrylates;

(b) flash vaporizing the component into the chamber;

(c) condensing a first layer of a film of vaporized component onto theouter surface of the container;

(d) curing the film;

(e) vaporizing an organosilicon component and admixing the volatilizedorganosilicon component with an oxidizer component and optionally aninert gas component to form a gas steam exterior to the chamber;

(f) establishing a glow discharge plasma in the chamber from one or moreof the gas stream components;

(g) controllably flowing the gas stream into the plasma while confiningat least a portion of the plasma therein;

(h) depositing a coating of silicon oxide adjacent the first layer;

(i) repeating steps (a) through (d) above, thereby depositing anacrylate coating on the silicon oxide coating; and

(j) repeating steps (e) through (h) above; thereby depositing a siliconoxide coating on said acrylate coating.

Optionally, the method further includes:

(k) dip coating PVDC on the silicon oxide coating.

Optionally, steps (i) through (j) may be repeated from about 1 to about10 times before dip coating PVDC on the silicon oxide coating.

Optionally, the container and/or the first layer may be flame-treated orplasma oxygen treated or corona discharge treated prior to applying thesecond layer coating.

Plastic tubes coated with the multi-layer barrier coating, comprisingthe primer coating, and an oxide layer and an overcoating layer are ableto maintain substantially far better vacuum retention, draw volume andtheir momechanical integrity retention than previous tubes comprised ofpolymer compositions and blends thereof without a coating of barriermaterials or of tubes comprising only an oxide coating. In addition, thetube's resistance to impact is much better than that of glass. Mostnotably is the clarity of the multi-layer coating and its durability tosubstantially withstand resistance to impact and abrasion.

Most preferably, the container of the present invention is a bloodcollection device. The blood collection device can be either anevacuated blood collection tube or a non-evacuated blood collectiontube. The blood collection tube is desirably made of polyethyleneterephthalate, polypropylene, polyethylene napthalate or copolymersthereof.

Printing may be placed on the multi-layer barrier coating applied to thecontainer of interest. For example, a product identification, bar code,brand name, company logo, lot number, expiration date and other data andinformation may all be included on the barrier coating. Moreover, amatte finish or a corona discharged surface may be developed on thebarrier coating so as to make the surface appropriate for writingadditional information on the label. Furthermore, a pressure sensitiveadhesive label may be placed over the barrier coating so as toaccommodate various hospital over-labels, for example.

Preferably, the multi-layer barrier coating of the present inventionprovides a transparent or colorless appearance and may have printedmatter applied thereon.

An advantage is that the method of the present invention provides areduction in the gas permeability of three-dimensional objects that hasnot been achieved with conventional deposition method typically usedwith thin films.

It has been found in the present invention that the acrylate organicmaterial, provides a good platform for the growth of the dense SiO_(x)barrier material.

It has been found that a highly crosslinked layer of acrylate improvesthe adhesion between a plastic surface and SiO_(x) and overall improvesthe thermomechanical stability of the coated system. In addition,acrylate primer coating has a role of a planarization (leveling) layer,covering the particles and imperfections on the surface of a polymer andreducing the defect density in the deposited inorganic coatings. Thegood bonding properties of the acrylate are also due to the fact thatarcylate is polar and the polarity provides means for good bondformation between the SiO_(x) and the acrylate. In addition, it has beenfound that a good bond formation is made between plastic tubes made ofpolypropylene and acrylate. Thus, the present invention provides themeans of substantially improving the barrier properties of polypropylenetubes. The adhesion properties of both the acrylate coating and theoxide coating can be further substantially improved by surfacepretreatment methods such as flame or oxygen plasma. Therefore, asignificant reduction in permeability of the article is due to thesubstantially improved SiO_(x) surface coverage that is obtained by theuse of a primer coating of acrylate on the plastic article surface.

The layer of PVDC improves the layer of SiO_(x) because it plugs thedefects and/or irregularities in the SiO_(x) coating. Furthermore, thePVDC coating improves the abrasion resistance of the SiO_(x) coating.

A plastic blood collection tube coated with the multi-layer barriercoating of the present invention will not interfere with testing andanalysis that is typically preformed on blood in a tube. Such testsinclude but are not limited to, routine chemical analysis, biologicalinertness, hematology, blood chemistry, blood typing, toxicologyanalysis or therapeutic drug monitoring and other clinical testsinvolving body fluids. Furthermore, a plastic blood collection tubecoated with the barrier coating is capable of being subjected toautomated machinery such as centrifuges and may be exposed to certainlevels of readiation in the sterilization process with substantially nochange in optical or mechanical and functional properties.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical blood collection tube with astopper.

FIG. 2 is a longitudinal sectional view of the tube of FIG. 1 takenalong line 2--2.

FIG. 3 is a longitudinal sectional view of a tube-shaped containersimilar to the tube of FIG. 1 without a stopper, comprising amulti-layer barrier coating.

FIG. 4 is a longitudinal sectional view of a tube-shaped container,similar to the tube of FIG. 1 with a stopper, comprising a multi-layerbarrier coating.

FIG. 5 is a longitudinal sectional view of a further embodiment of theinvention illustrating the tube with a stopper similar to FIG. 1 andwith the multi-layer barrier coating encompassing both the tube andstopper thereof.

FIG. 6 illustrates an enlarged partially sectioned, diagram of a flashevaporator apparatus.

FIG. 7 illustrates a plasma deposition system.

FIG. 8 is a general schematic diagram illustrating the layers depositedon the substrate.

DETAILED DESCRIPTION

The present invention may be embodied in other specific forms and is notlimited to any specific embodiment described in detail which is merelyexemplary. Various other modifications will be apparent to and readilymade by those skilled in the art without departing from the scope andspirit of the invention. The scope of the invention will be measured bythe appended claims and their equivalents.

Referring to the drawings in which like reference characters refer tolike parts throughout the several views thereof, FIGS. 1 and 2 show atypical blood collection tube 10, having a sidewall 11 extending from anopen end 16 to a closed end 18 and a stopper 14 which includes a lowerannular portion or skirt 15 which extends into and presses against theinner surface 12 of the sidewall for maintaining stopper 14 in place.

FIG. 2 schematically illustrates that there are three mechanisms for achange in vacuum in a blood collection tube: (A) gas permeation throughthe stopper material; (B) gas permeation through the tube and (C) leakat the stopper tube interface. Therefore, when there is substantially nogas permeation and no leak, there is good vacuum retention and good drawvolume retention.

FIG. 3 shows the preferred embodiment of the invention, a plastic tubecoated with at least two layers of barrier materials. The preferredembodiment includes many components which are substantially identical tothe components of FIGS. 1 and 2. Accordingly, similar componentsperforming similar functions will be numbered identically to thosecomponents of FIGS. 1 and 2, except that a suffix "a" will be used toidentify those components in FIG. 3.

Referring now to FIG. 3, the preferred embodiment of the invention,collection tube assembly 20 comprises a plastic tube 10a, having asidewall 11a extending from an opened end 16a to a closed end 18a. Abarrier coating 25 extends over a substantial portion of the outersurface of the tube with the exception of open end 16a. Barrier coating25 comprises a first layer 26 of polymer material such as an acrylate, asecond layer 27 of a multiple sequence of inorganic and organic coatingsand a third layer 28 of an organic overcoating layer such as PVDC.

The second layer preferably comprises a multiple sequence of coatingsexpressed as follows: ##EQU2## where n=0-10.

FIG. 4 illustrates an alternate embodiment of the invention, whereincollection tube assembly 40 comprises stopper 48 in place for closingopen end 41 of tube 42. As can be seen, sidewall 43 extends from openend 41 to closed end 44 and stopper 48 includes an annular upper portion50 which extends over the top edge of tube 42. Stopper 48 includes alower annular portion or skirt 49 which extends into and presses againstthe inside inner surface 46 of sidewall 43 for maintaining stopper 48 inplace. Also, the stopper has a septum portion 52 for receiving a cannulatherethrough.

Thus, the user, once receiving a container such as that shown in FIG. 4with a sample contained therein, may insert a cannula through septum 52for receiving part or all of the contents in tube 42 to perform varioustests on a sample. Covering a substantial portion of the length of thetube is a multi-layer barrier coating 45. Multi-layer barrier coating 45covers substantially most of the tube with the exception of open end 41thereof. Multi-layer barrier coating 45 comprises a first layer 54 of apolymer material, a second layer 56 of multiple sequence of inorganicand organic materials such as silicone oxide and acrylate and a thirdlayer 57 of an organic barrier material such as PVDC. FIG. 4 differsfrom the embodiment in FIG. 3 in that the tube may be evacuated with thesimultaneous placement of stopper 48 therein after the application oflayers 54 and 56 over the tube. Alternatively, the multi-layer barriercoating may be applied to the tube after it has been evacuated.

FIG. 5 shows an additional embodiment of the barrier coating and a tube.The alternate embodiment functions in a similar manner to the embodimentillustrated in FIG. 4. Accordingly, similar components performingsimilar functions will be numbered identically to those components inthe embodiment of FIG. 4, except that a suffix "a" will be used toidentify those components in FIG. 5.

Referring now to FIG. 5, a further embodiment 60 of the inventionwherein multi-layer barrier coating 45a incorporates both upper portion50a of stopper 48a, as well as the entire outer surface of tube 42a.Multi-layer barrier coating 45a includes serrations 62 at the tube,stopper interface. The serrations are registered so that it can bedetermined if the sealed container has been tampered with. Such anembodiment may be utilized, for example, for sealing the container withthe stopper in place. Once a sample has been placed in the tube, thesample cannot be tampered with by removal of the stopper. Additionally,the serrations may be registered so that it can be determined if thesealed container has been tampered with. Such an arrangement may beappropriate, for example, in drug abuse testing, specimen identificationand quality control.

In an alternate embodiment of the invention, multi-layer barrier coating45 is repeatedly or sequentially applied to the inner and/or outersurface of the tube. Preferably, the coating is applied at least twice.

It will be understood by practitioners-in-the-art, that such tubes maycontain reagents in the form of additives or coatings on the inner wallof the tube.

The multi-layer barrier coating forms a substantially clear ortranslucent barrier. Therefore, the contents of a plastic tube with amulti-layer barrier coating comprising at least two layers of barriermaterials are substantially visible to the observer at the same timeidentifying information may be displayed over the multi-layer barriercoating after it is applied to the plastic tube.

The first layer of the multi-layer barrier coating may be formed on thetube by dip-coating, roll-coating or spraying acrylate monomer or theblend of monomers, followed by UV curing process.

The acrylate polymer material may also be applied to the tube by anevaporation and curing process carried out as described in U.S. Pat. No.5,032,461, the disclosure of which is herein incorporated by reference.

The acrylate evaporation and curing process involves first atomizing theacrylate monomer into about 50 micron droplets and then flashing themoff of a heated surface. This produces an acrylate molecular vapor whichhas the same chemistry as the starting monomer.

Acrylates are available with almost any chemistry desired. They usuallyhave either one, two or three acrylate groups per molecule. Variousmixtures of mono, di and tri acrylates are useful in the presentinvention. Most preferable are monoacrylates and diacrylates.

Acrylates form one of the most reactive classes of chemicals. They curerapidly when exposed to UV or electron beam radiation to form across-linked structure. This imparts high temperature and abrasionresistant properties in the coating.

The monomer materials utilized are relatively low in molecular weight,between 150 and 1,000 and preferably in the range of 200 to 300 and havevapor pressures between about 1×10⁻ Torr and 1×10⁻¹ Torr at standardtemperature and pressure (i.e., relatively low boiling materials). Avapor pressure of about 1×10⁻² Torr is preferred. Polyfunctionalacrylates are especially preferred. The monomers employed have at leasttwo double bonds (i.e., a plurality of olefinic groups). Thehigh-vapor-pressure monomers used in the present invention can bevaporized at low temperatures and thus are not degraded (cracked) by theheating process. The absence of unreactive degradation products meansthat films formed from these low molecular weight, high-vapor-pressuremonomers have reduced volatile levels of components. As a result,substantially all of the deposited monomer is reactive and will cure toform an integral film when exposed to a source of radiation. Theseproperties make it possible to provide substantially continuous coatingdespite the fact that the film is very thin. The cured film exhibitsexcellent adhesion and are resistant to chemical attack by organicsolvents and inorganic salts.

Because of their reactivity, physical properties and the properties ofcured films formed from such components, polyfunctional acrylates areparticularly useful monomeric materials. The general formula for suchpolyfunctional acrylates is: ##STR1## wherein: R¹ is an aliphatic,alicyclic or mixed aliphatic-alicyclic radical;

R² is a hydrogen, methyl, ethyl, propyl, butyl or pentyl; and

n is from 2 to 4.

Such polyfunctional acrylates may also be used in combination withvarious monacrylates, such as those having the formula: ##STR2##wherein: R², is as defined above;

X¹ is H, epoxy, 1,6-hexanediol, tripropyleneglycol or urethane; and

r, s are 1-18. ##STR3## X³ is CN or COOR³ wherein R³ is an alkyl radicalcontaining 1-4 carbon atoms. Most often, X³ is CN or COOCH₃.

Diacrylates of the formula below are particularly preferred: ##STR4##wherein: X₁, r and s are as defined above.

Curing is accomplished by opening the double bonds of the reactantmolecules. This can be accomplished by means of an energy source such asapparatus which emits infrared, electrons or ultraviolet radiation.

FIG. 6 illustrates the process for applying an acrylate coating. Anacrylate monomer 100 is directed through a dielectric evaporator 102 andthen through an ultrasonic atomizer 104 and into a vacuum chamber 106.The monomer droplets are atomized ultrasonically and the dropletsvaporized where they condense on the rotating tube or film that isloaded on a drum 108.

The condensed monomer liquid subsequently is radiation cured by means ofan electron beam gun 110.

The second layer of the multi-layer barrier coating, an inorganicmaterial, may be formed over the acrylate coating by radio frequencydischarge, direct or dual ion beam deposition, sputtering or plasmachemical vapor deposition, as described in U.S. Pat. Nos. 4,698,256,4,809,876, 4,992,298 and 5,055,318, the disclosures of which are hereinincorporated by reference.

For example, a method of depositing an oxide coating is provided byestablishing a glow discharge plasma in a previously evacuated chamber.The plasma is derived from one or more of the gas stream components, andpreferably is derived from the gas stream itself. The article ispositioned in the plasma, preferably adjacent the confined plasma, andthe gas stream is controllably flowed into the plasma. A silicon oxidebased film is deposited on the substrate to a desired thickness. Thethickness of the oxide coating is about 100 Angstroms (Å) to about10,000 Å. A thickness of less than about 5,000 Å may not providesufficient barrier and a thickness of greater than about 5,000 Å maycrack, thus decreasing the effective barrier. Most preferably, thethickness of the oxide coating is about 1,000 Å to about 3,000 Å.

Another method of depositing an oxide coating is by confining a plasmawith magnets. Preferably, the magnetically enhanced method fordepositing a silicon oxide based film on a substrate is preferablyconducted in a previously evacuated chamber of glow discharge from a gasstream. The gas stream preferably comprises at least two components: avolatilized organosilicon component, an oxidizer component such asoxygen, nitrous oxide, carbon dioxide or air and an optionally inert gascomponent.

Examples of suitable organosilicon compounds useful for the gas streamin the plasma deposition methods are liquid or gas at about ambienttemperature and when volatilized have a boiling point about 0° C. toabout 150° C. and include dimethysilane, trimethylsilane, diethylsilane,propylsilane, phenylsilane, hexamethyldisilane,1,1,2,2-tetramethyldisilane, bis(trimethylsilane)methane,bis(dimethylsilyl)methane, hexamethyldisiloxane, vinyl trimethoxysilane, vinyl triethyoxysilane, ethylmethoxysilane,ethyltrimethoxysilane, divinyltetramethyldisiloxane, hexamethyldsilazanedivinyl-hexamethyltrisiloxane, trivinylpentamethyltrisiloxazane,tetraethoxysilane and tetramethoxysilane.

Among the preferred organosilicons are 1,1,3,3-tetramethyldisiloxane,trimethylsilane, hexamethyldisiloxane, vinyltrimethylsilane,methyltrimethoxysilane, vinyltrimethoxysilane and hexamethyldisilazane.These preferred organosilicon compounds have boiling points of 71° C.,55.5° C., 102° C., 123° C. and 127° C. respectively.

The optional inert gas of the gas stream preferably is helium, argon ornitrogen.

The volatilized organosilicon component is preferably admixed with theoxygen component and the inert gas component before being flowed intothe chamber. The quantities of these gases being so admixed arecontrolled by flow controllers so as to adjustably control the flow rateratio of the gas stream components.

Various optical methods known in the art may be used to determine thethickness of the deposited film while in the deposition chamber, or thefilm thickness can be determined after the article is removed from thedeposition chamber.

The deposition method of the present invention is preferably practicedat relatively high power and quite low pressure. A pressure less thanabout 500 millitorr (mTorr) should be maintained during the deposition,and preferably the chamber is at a pressure between about 43 to about490 millitorr during the deposition of film. Low system pressure resultsin lower deposition rates whereas higher system pressure provides fasterdeposition rates. When the plastic article to be coated is heatsensitive, a higher system pressure may be used to minimize the amountof heat the substrate is exposed to during deposition because highsubstrate temperatures are to be avoided for low Tg polymers such aspolypropylene and PET (Tg is -10° C. and 60° C. respectively).

The substrate is electrically isolated from the deposition system(except for electrical contact with the plasma) and is at a temperatureof less than about 80° C. during the depositing. That is, the substrateis not deliberately heated.

Referring to FIG. 7, the system for depositing a silicon oxide basedfilm comprises an enclosed reaction chamber 170 in which a plasma isformed and in which a substrate or tube 171, is placed for depositing athin film of material on a sample holder 172. The substrate can be anyvacuum compatible material, such as plastic. One or more gases aresupplied to the reaction chamber by a gas supply system 173. An electricfield is created by a power supply 174.

The reaction chamber can be of an appropriate type to perform any of theplasma-enhanced chemical vapor deposition (PECVD) or plasmapolymerization process. Furthermore, the reaction chamber may bemodified so that one or more articles may be coated with an oxide layersimultaneously within the chamber.

The pressure of the chamber is controlled by a mechanical pump 188connected to chamber 170 by a valve 190.

The tube to be coated is first loaded into chamber 170 in sample holder172. The pressure of the chamber is reduced to about 5 m Torr bymechanical pump 188. The operating pressure of the chamber is about 90to about 140 mTorr for a PECVD or plasma polymerization process and isachieved by flowing the process gases, oxygen and trimethyl silane, intothe chamber through monomer inlet 176.

The thin film is deposited on the outer surface of the tube and has adesired uniform thickness or the deposition process may be interruptedperiodically to minimize heating of the substrate and/or electrodesand/or physically remove particulate matter from the articles.

Magnets 196 and 198 are positioned behind electrode 200 to create anappropriate combination of magnetic and electrical fields in the plasmaregion around the tube.

The system is suitable for low frequency operation. An example frequencyis 40 kHz. However, there can be some advantages from operating at amuch high frequency, such as in the radio frequency range of severalmegahertz.

The silicon oxide based film or blends thereof used in accordance withthis disclosure, may contain conventional additives and ingredientswhich do not adversely affect the properties of articles made therefrom.

The third layer of the multi-layer barrier coating may be formed on thesecond layer by dip-coating, roll-coating or spraying an agueousemulsion of the polyoinylidene chloride or homo or co-polymers, followedby air drying.

The third layer may preferably be vinylidenechloride-acrylonitrile-methyl methacrylate-methyl acrylate-acrylic acidcopolymers, thermosetting epoxy coatings, parylene polymers, orpolyesters.

Preferably, the third layer is a parylene polymer. Parylene is thegeneric name for members of the polymer series developed by UnionCarbide Corporation. The base member of the series, called parylene N,is poly-p-exlylene, a linear, crystalline material: ##STR5##

Parylene C, a second member of the parylene series is produced from thesame monomer as parylene N and modified by the substitution of achlorine atom for one of the aromatic hydrogens: ##STR6##

Parylene D, the third member of the parylene series is produced from thesame monomer as parylene N and modified by the substitution of thechlorine atom for two of the aromatic hydrogens: ##STR7##

Most preferably, the polymer layer is a vinylidene chloride-methylmethacrylate-methacrylate acrylic acid polymer (PVDC). This polymer isavailable as DARAN® 8600-C (trademark of W. R. Grace and Co.) sold byGRACE, Organic Chemicals Division, Lexington, Mass.

The third layer of the barrier coating, a polymer material, may be aparylene polymer applied to the second layer by a process similar tovacuum metallizing, as described in U.S. Pat. Nos. 3,342,754 and3,300,332, the disclosures of which are herein incorporated byreference. Alternatively, the third layer may be vinylidenechloride-acrylonitrile-methyl methacrylate-methyl acrylate-acid acrylicpolymer, applied to the second layer by dip-coating, roll-coating orspraying an aqueous emulsion of the polymer, followed by air drying ofthe coating, as described in U.S. Pat. Nos. 5,093,194 and 4,497,859, thedisclosure of which are herein incorporated by reference.

As shown in FIG. 8, the acrylate coating A and the silicon oxide basedcoating B may have defects or irregularities C. It is believed thatcomplete coverage of the substrate D cannot be achieved with only thesilicon oxide based coatings and acrylate coatings. Although the defectsand irregularities are substantialy minimized with the sequence ofsilicon oxide and acrylate coatings, a final coating of PVDC, E, may beapplied over the last silicon oxide coating to produce a completebarrier coating over the substrate surface.

A variety of substrates can be coated with a barrier coating by theprocess of the present invention. Such substrates include, but are notlimited to packaging, containers, bottles, jars, tubes and medicaldevices.

A plastic blood collection tube coated with the multi-layer barriercoating will not interfere with testing and analysis that is typicallyperformed on blood in a tube. Such tests include but are not limited to,routine chemical analysis, biological inertness, hematology, bloodchemistry, blood typing, toxicology analysis or therapeutic drugmonitoring and other clinical tests involving body fluids. Furthermore,a plastic blood collection tube coated with the barrier coating iscapable of being subjected to automated machinery such as centrifugesand may be exposed to certain levels of radiation in the sterilizationprocess with substantially no change in optical or mechanical andfunctional properties.

A plastic blood collection tube coated with the multi-layer barriercoating is able to maintain 90% original draw volume over a period ofone year. Draw volume retention depends on the existence of a particlevacuum, or reduced pressure, inside the tube. The draw volume changes indirect proportion to the change in vacuum (reduced pressure). Therefore,draw volume retention is dependent on good vacuum retention. A plastictube coated with a barrier coating substantially prevents gas permeationthrough the tube material so as to maintain and enhance the vacuumretention and draw volume retention of the tube. Plastic tubes withoutthe multi-layer coating of the present invention may maintain about 90%draw volume for about 3 to 4 months.

If the multi-layer barrier coating is also coated or applied on theinner surface of the plastic blood collection tube, the barrier coatingmay be hemorepellent and/or have characteristics of a clot activator.

It will be understood that it makes no difference whether the plasticcomposite container is evacuated or not evacuated in accordance withthis invention. The presence of a barrier coating on the outer surfaceof the container has the effect of maintaining the general integrity ofthe container holding a sample so that it may be properly disposed ofwithout any contamination to the user. Notable is the clarity of thebarrier coating as coated or applied on the container and its abrasionand scratch resistance.

The barrier coating used in accordance with this disclosure, maycontainer conventional additives and ingredients which do not adverselyaffect the properties of articles made therefrom.

The following examples are not limited to any specific embodiment of theinvention, but are only exemplary.

EXAMPLE 1 Method for Coating Plastic Substrates Tubes With Multi-LayerBarrier Coating

An acrylate coating was applied to polypropylene tubes and films(substrates) of various thickness in a chamber wherein TripropyleneGlycol Diacrylate (TPGDA) was fed into the evaporator and was flashvaporized at about 343° C. onto the substrate in the chamber andcondensed. The condensed monomer film was then E-beam cured by anelectron beam gun.

The substrate coated with the acrylate coating (TPGDA) was then cleanedwith a mixture comprising equal parts of a micro detergent andde-ionized (DI) water solution. The substrate was rinsed thoroughly inDI water and allowed to air dry. The cleaned substrate was then storedin a vacuum oven at room temperature until it was to be coated.

The cleaned substrate was then attached to a holder which fits midwaybetween the electrodes in the glass vacuum chamber. The chamber wasclosed and a mechanical pump was used to achieve a base pressure of 5mTorr.

The electrode configuration is internally capacitively coupled withpermanent magnets on the backside of the titanium electrodes. Thisspecial configuration provides the ability to confine the glow betweenthe electrodes because of the increase in collision probability betweenelectrons and reacting gas molecules. The net result of applying amagnetic field is similar to increasing the power applied to theelectrodes, but without the disadvantages of higher bombardment energiesand increased substrate heating. The use of magnetron discharge allowsoperation in the low pressure region and a substantial increase inpolymer deposition rate.

The monomer which consists of a mixture of trimethylsilane (TMS) andoxygen was introduced through stainless steel tubing near theelectrodes. The gases were mixed in the monomer inlet line beforeintroduction into the chamber. Flow rates were manually controlled bystainless steel metering valves. A power supply operating at an audiofrequency of 40 kHz was used to supply power to the electrodes. Thesystem parameters used for thin film deposition of plasma polymerizedTMS/O₂ on the polymer substrate were as follows:

    ______________________________________                                        Surface Pretreatment:                                                                       TMS Flow    =     0 sccm                                                      Base Pressure                                                                             =     5 mTorr                                                     Oxygen Flow =     10 sccm                                                     System Pressure                                                                           =     140 mTorr                                                   Power       =     50 watts                                                    Time        =     2 minutes                                     Oxide Deposition:                                                                           TMS Flow    =     0.75-1.0 sccm                                               Oxygen Flow =     2.5 = 3.0 sccm                                              System Pressure                                                                           =     90-100 mTorr                                                Power       =     30 watts                                                    Deposition Time                                                                           =     5 minutes                                     ______________________________________                                    

After the thin film was deposited, the reactor was allowed to cool. Thereactor was then opened, and the substrate was removed.

The process of applying the acrylate coating followed by oxidedeposition was then repeated.

A protective topcoating of a water-based emulsion of PVDC copolymer wasthen applied by dip coating and cured at 65° C. for 10 minutes toproduce a final coating thickness averaging about 6 microns.

EXAMPLE 2 Method for Coating Plastic Substrates With Multi-Layer BarrierCoating

An acrylate coating was applied to polypropylene tubes and films(substrates) in a chamber wherein a 60:40 mixture of isobornylacrylate:epoxydiacrylate (IBA:EDA) was fed into the evaporator and flashvaporized at about 343° C. onto the substrate in the chamber andcondensed. The condensed monomer film was then UV cured by an actiniclight source of 365 nm.

The substrate coated with the acrylate coating (IBA:EDA) was thencleaned with a mixture comprising equal parts of a micro detergent andde-ionized (DI) water solution. The substrate was rinsed thoroughly inDI water and allowed to air dry. The cleaned substrate was then storedin a vacuum oven at room temperature until it was to be coated.

The cleaned substrate was then attached to a holder which fits midwaybetween the electrodes in the glass vacuum chamber. The chamber wasclosed and a mechanical pump was used to achieve a base pressure of 5mTorr.

The electrode configuration is internally capacitively coupled withpermanent magnets on the backside of the titanium electrodes. Thespecial configuration provides the ability to confine the glow betweenthe electrodes because of the increase in collision probability betweenelectrons and reacting gas molecules. The net result of applying amagnetic field is similar to increasing the power applied to theelectrodes, but without the disadvantages of higher bombardment energiesand increased substrate heating. The use of magnetron discharge allowsoperation in the low pressure region and a substantial increase inpolymer deposition rate.

The monomer which consists of a mixture of trimethylsilane (TMS) andoxygen was introduced through stainless steel tubing near theelectrodes. The gases were mixed in the monomer inlet line beforeintroduction into the chamber. Flow rates were manually controlled bystainless steel metering valves. A power supply operating at an audiofrequency of 40 kHz was used to supply power to the electrodes. Thesystem parameters used for thin film deposition of plasma polymerizedTMS/O₂ on the polymer substrate were as follows:

    ______________________________________                                        Surface Pretreatment:                                                                       TMS Flow    =     0 sccm                                                      Base Pressure                                                                             =     5 mTorr                                                     Oxygen Flow =     10 sccm                                                     System Pressure                                                                           =     140 mTorr                                                   Power       =     50 watts                                                    Time        =     2 minutes                                     Oxide Deposition:                                                                           TMS Flow    =     0.75-1.0 sccm                                               Oxygen Flow =     2.5 = 3.0 sccm                                              System Pressure                                                                           =     90-100 mTorr                                                Power       =     30 watts                                                    Deposition Time                                                                           =     5 minutes                                     ______________________________________                                    

After the thin film was deposited, the reactor was allowed to cool. Thereactor was then opened, and the substrate with a multi-layer barriercoating was removed.

The process of applying the acrylate coating followed by oxidedeposition was repeated.

A protective topcoating of a water-based emulsion of PVDC copolymer wasthen applied by dip coating anc cured at 65° C. for 10 minutes toproduce a final coating thickness averaging about 6 microns.

EXAMPLE 3 Comparison of Substrates With and Without Multi-Layer BarrierCoatings

All of the substrates prepared in accordance with Examples 1 and 2 abovewere evaluated for oxygen permeance (OTR) in the oxide coatings asfollows.

(i) Oxygen Permeance (OTR)

Film or plaque samples were tested for oxygen permeance (OTR) using a MOCON Ox-TARN 2/20 (sold by Modern Controls, Inc., 7500 Boone Avenue N.,Minneapolis, Minn. 55428). A single side of the film sample was exposedto 1 atm of 100% oxygen atmosphere. Oxygen permeating through the samplefilm was entrained in a nitrogen carrier gas stream on the opposite sideof the film, and detected by a coulmetric sensor. An electrical signalwas produced in proportion to the amount of oxygen permeating throughthe sample. Samples were tested at 30° C. and 0% relative humidity(R.H.). Samples were conditioned for 1 to 20 hours prior to determiningoxygen permeance. The results are reported in Table 1 in units ofcc/m2-atm-day.

Tube samples were tested for oxygen permeance (OTR) using a MOCON O_(x)-TRAN 1,000 (sold by Modem Controls, Inc., 7500 Boone Avenue N.,Minneapolis, Minn. 55428). A package adapter was used for mounting thetubes in a manner that allowed the outside of the tube to be immersed ina 100% O₂ atmosphere while the inside of tube is flushed with a nitrogencarrier gas. The tubes were then tested at 20° C. and 50% R.H. The tubeswere allowed to equilibrate for 2-14 days before a steady statepermeability is determined. The results are reported in Table 1 in unitsof cc/m² -atm-day.

                                      TABLE 1                                     __________________________________________________________________________                                  Oxygen Transmission                                     Acrylate                                                                           SiO.sub.X                                                                         Acrylate                                                                           SiO.sub.X                                                                         PVDC                                                                              (cc/m.sup.2 -atm-day                            Sample  Coating                                                                            Coating                                                                           Coating                                                                            Coating                                                                           Coating                                                                           30° , 0% RH                              __________________________________________________________________________    PP film, control                                                                      no   no  no   no  no  1500                                            PP plaque                                                                             no   yes no   no  no  37                                              PP plaque                                                                             TPGDA                                                                              yes no   no  no  3.5                                             PP plaque                                                                             no   no  no   no  no  65                                              PP plaque                                                                             yes  yes no   no  yes 0.04                                            PP tube, control                                                                      no   no  no   no  no  70                                              PP tube IBA:DA                                                                             no  no   no  no  70                                              PP tube no   yes no   no  no  46-60                                           PP tube IBA:DA                                                                             yes no   no  no  4.3-6.4                                         PP tube IBA:DA                                                                             yes no   no  yes 2.5                                             PP tube TPGDA                                                                              yes no   no  yes 5                                               PC film, control                                                                      no   no  no   no  no  1700                                            PC film 110  no  no   no  no  559                                             PC film 110  yes no   no  no  6.4-8.3                                         PC film 110  yes 110  yes no  0.1-0.2                                         PC film no   yes no   no  no  8                                               __________________________________________________________________________     IBA:DA = isonorbornyl: epoxydiacrylate (60:40), UV cured                      TPGDA = tripropylene glycol diacrylate Ebeam cured                            SiO.sub.X Coating = 1000-3000 Angstroms (as measured by Scanning Electron     Microscope)                                                                   PC = polycarbonate                                                            PP = polypropylene                                                            plaque = 75 mil thickness                                                     film = 3 mil thickness                                                        tubes = nominal wall thickness of 40 mil                                      110 = crosslinkable acrylate, uv cured                                   

What is claimed is:
 1. A method of depositing a multilayer barriercoating on a plastic substrate comprising:(a) selecting a curablecomponent comprising: i) polyfunctional acrylates, or ii) mixtures ofmonoacrylates and polyfunctional acrylates; (b) flash vaporizing saidcomponent into said chamber; (c) condensing a first layer of an acrylatefilm of said vaporized component onto the outer surface of saidsubstrate; (d) curing said acrylate film; (e) vaporizing anorganosilicon component and admixing a volatilized organosiliconcomponent with an oxidizer component and optionally an inert gascomponent to form a gas stream exterior to the chamber; (f) establishinga glow discharge plasma in the chamber from one or more of the gasstream components; (g) controllably flowing the gas stream into theplasma while confining at least a portion of the plasma therein; (h)depositing a coating of silicon oxide adjacent said first layer; (i)repeating steps (a) through (d) above, thereby depositing an acrylatecoating on said silicon oxide coating; and (j) repeating steps (e)through (h) above, thereby depositing a silicon oxide coating on saidacrylate coating.
 2. The method of claim 1 further comprising:(k) dipcoating poly(vinylidene chloride) on said silicon oxide coating.
 3. Themethod of claim 1 further comprising:(k) repeating steps (i) through (j)from about 1 to about 10 times.
 4. The method of claim 3 furthercomprising:(l) dip coating poly(vinylidene chloride) on said siliconoxide coating.
 5. The method of claim 1 wherein said first layer of saidacrylate coating is pretreated by oxygen plasma.